Analog Devices Inc. LT3689EMSE-5#PBF

Overview

LT3689EMSE-5#PBF from Analog Devices (formerly Linear Technology) is a 700mA monolithic step-down switching regulator with integrated power-on reset (POR) and pin-selectable watchdog timer (window or timeout mode), operating from 3.6V to 36V input, delivering fixed 5V output with ±1% accuracy over temperature, 85µA quiescent current in Burst Mode®, and robust 60V transient tolerance - deployed in automotive ECU power rails and industrial microcontroller supervision.

For engineers reviewing the LT3689EMSE-5#PBF datasheet, LT3689EMSE-5#PBF pinout, LT3689EMSE-5#PBF application, or LT3689EMSE-5#PBF equivalent, this page delivers verified package mapping (16-pin MSOP with exposed pad), confirmed 5V fixed-output regulation, validated watchdog timing equations (tWDU = 18.2 × CWDT, tWDL = 0.588 × CWDT), and real-world design constraints including minimum on-time (130ns), frequency foldback behavior, and DA-pin current-limiting at 1.2A.

Technical Context

The LT3689EMSE-5#PBF implements constant-frequency current-mode PWM control with internal NPN switch, programmable 350kHz–2.2MHz switching via RT resistor, and automatic transition to low-ripple Burst Mode® below ~10mA load - maintaining <15mV_P-P output ripple and 85µA I_Q. Its POR comparator asserts RST low when V_OUT drops below 90% of 5V (i.e., 4.5V), then releases after CPOR-programmed delay (e.g., 157ms with 68nF).

Watchdog operation is configurable via W/T pin: timeout mode triggers WDO low if no WDI edge occurs within tWDU; window mode triggers WDO low if successive WDI falling edges violate tWDL–tWDU bounds. Both periods scale linearly with CWDT capacitance (tWDU = 18.2 ms/nF, tWDL = 0.588 ms/nF), with glitch-immune thresholds (WDI: 0.4–1.15V, W/T: 0.4–1V) and open-drain outputs (RST/WDO) pulled weakly to V_OUT.

Key Specifications

Pinout & Package

LT3689EMSE-5#PBF uses a 16-lead plastic MSOP package with exposed thermal pad (pin 17 = GND), θ_JA = 43°C/W, requiring soldered pad for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator with supervisory functions applications.

Compared with LT3689EMSE#PBF, the LT3689EMSE-5#PBF saves board space and improves accuracy by eliminating feedback resistors, while MAX5033AASA+T reduces component count only if external supervision is acceptable - making LT3689EMSE-5#PBF optimal for space-constrained, safety-aware designs requiring guaranteed 5V and hardware watchdog.

Availability

LT3689EMSE-5#PBF is available at Aetrix Electronics and suitable for automotive electronic control units, industrial programmable logic controllers, and medical infusion pump controllers requiring stable component supply, long-term lifecycle support, and AEC-Q100-compliant alternatives.

Supply support for LT3689EMSE-5#PBF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices acquired Linear Technology in 2017, inheriting its legacy of high-performance power management ICs with emphasis on precision, reliability, and ruggedness in harsh environments.

The LT3689 product line was designed specifically for automotive and industrial applications demanding integrated power conversion plus microprocessor supervision - combining robust 60V transient tolerance, accurate POR, and configurable watchdog functionality in a single monolithic IC.

FAQ

What is the output voltage tolerance of the LT3689EMSE-5#PBF over temperature?

The LT3689EMSE-5#PBF delivers a fixed 5.00V output with ±1% tolerance (4.95V to 5.05V) across its full operating junction temperature range of –40°C to 125°C, as specified in the Electrical Characteristics table under "LT3689-5 Output Voltage." This accuracy is factory-trimmed and does not require external components, unlike the adjustable LT3689EMSE#PBF variant.

How do I configure the LT3689EMSE-5#PBF for window-mode watchdog operation?

To configure the LT3689EMSE-5#PBF for window-mode watchdog, tie the W/T pin (pin 14) to GND. In this mode, the LT3689EMSE-5#PBF monitors consecutive falling edges on the WDI pin and asserts WDO low if any two edges occur either too close together (violating tWDL) or too far apart (exceeding tWDU), both determined by the CWDT capacitor value.

What is the minimum recommended capacitor value for CPOR to achieve a 100ms reset timeout on the LT3689EMSE-5#PBF?

The LT3689EMSE-5#PBF uses a scaling factor of 2.3ms per nanofarad on the CPOR pin. To achieve a 100ms reset timeout, use CPOR = 100ms ÷ 2.3ms/nF ≈ 43.5nF - a standard 43nF or 47nF 1% X7R ceramic capacitor (e.g., Murata GRM188R71E473KA01) is recommended for stability and temperature performance.

Does the LT3689EMSE-5#PBF require an external catch diode, and what are the key selection criteria?

Yes, the LT3689EMSE-5#PBF requires an external Schottky catch diode connected between SW and GND. Key selection criteria include: 40V+ reverse voltage rating (to handle 60V transients), ≤0.5V forward voltage at 700mA, low reverse leakage (<5µA at 125°C), and thermal compatibility with the MSOP layout. Diodes Inc. B140HB is a validated option per the datasheet's typical application.

Can the LT3689EMSE-5#PBF synchronize to an external clock, and what are the timing requirements?

Yes, the LT3689EMSE-5#PBF supports external synchronization via the SYNC pin (pin 10). The input must be a logic-level signal with minimum positive and negative pulse widths of 80ns each. The internal RT-set frequency must be at least 20% lower than the lowest expected sync frequency to ensure reliable locking - for example, set RT for 800kHz when syncing to a 1MHz clock.